title: Inhibition of P-glycoprotein-mediated paclitaxel resistance by reversibly linked quinine homodimers.
abstract: P-glycoprotein (P-gp), an ATP-dependent drug efflux pump, has been implicated in multidrug resistance of several cancers as a result of its overexpression. In this work, rationally designed second-generation P-gp inhibitors are disclosed, based on dimerized versions of the substrates quinine and quinidine. These dimeric agents include reversible tethers with a built-in clearance mechanism. The designed agents were potent inhibitors of rhodamine 123 efflux in cultured cancer cell lines that display high levels of P-gp expression at the cell surface and in transfected cells expressing P-gp. The quinine homodimer Q2, which was tethered by reversible ester bonds, was particularly potent (IC(50) approximately 1.7 microM). Further studies revealed that Q2 inhibited the efflux of a range of fluorescent substrates (rhodamine 123, doxorubicin, mitoxantrone, and BODIPY-FL-prazosin) from MCF-7/DX1 cells. The reversibility of the tether was confirmed in experiments showing that Q2 was readily hydrolyzed by esterases in vitro (t(1/2) approximately 20 h) while demonstrating high resistance to nonenzymatic hydrolysis in cell culture media (t(1/2) approximately 21 days). Specific inhibition of [(125)I]iodoarylazidoprazosin binding to P-gp by Q2 verified that the bivalent agent interacted specifically with the drug binding site(s) of P-gp. Q2 was also an inhibitor of verapamil-stimulated ATPase activity. In addition, low concentrations of Q2 stimulated basal P-gp ATPase levels. Finally, Q2 was shown to inhibit the transport of radiolabeled paclitaxel (Taxol) in MCF-7/DX1 cells, and it completely reversed the P-gp-mediated paclitaxel resistance phenotype.
authors.affiliation: Department of Chemistry and Purdue Cancer Center, Purdue University, West Lafayette, Indiana, USA.
authors.forename: Marcos M
authors.initials: MM
authors.lastname: Pires
authors.forename: Dana
authors.initials: D
authors.lastname: Emmert
authors.forename: Christine A
authors.initials: CA
authors.lastname: Hrycyna
authors.forename: Jean
authors.initials: J
authors.lastname: Chmielewski
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors*; D000230:Adenocarcinoma / Q000473:pathology; D000251:Adenosine Triphosphatases / Q000032:analysis / Q000378:metabolism; D000345:Affinity Labels; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004317:Doxorubicin / Q000378:metabolism; D018432:Drug Resistance, Multiple / Q000187:drug effects*; D019008:Drug Resistance, Neoplasm; D005260:Female; D005434:Flow Cytometry; D005456:Fluorescent Dyes / Q000378:metabolism; D006801:Humans; D020128:Inhibitory Concentration 50; D015394:Molecular Structure; D017239:Paclitaxel / Q000378:metabolism*; D011224:Prazosin / Q000378:metabolism; D011803:Quinine / Q000737:chemistry* / Q000494:pharmacology*; D020112:Rhodamine 123 / Q000378:metabolism; D014700:Verapamil / Q000378:metabolism
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000345:Affinity Labels; D005456:Fluorescent Dyes; D020112:Rhodamine 123; D004317:Doxorubicin; D011803:Quinine; D014700:Verapamil; D000251:Adenosine Triphosphatases; D017239:Paclitaxel; D011224:Prazosin